Electrochemical carbon monoxide production

ABSTRACT

A method and apparatus for producing a carbon monoxide containing product in which cathode and anode sides of an electrically driven oxygen separation device are contacted with carbon dioxide and a reducing agent, respectively. The carbon dioxide is reduced to carbon monoxide through ionization of oxygen and the reducing agent lowers the partial pressure of oxygen at the anode side to partially drive oxygen ion transport within the device through the consumption of the oxygen and to supply heat. The lowering of oxygen partial pressure reduces voltage and therefore, electrical power required to be applied to the device and the heat is supplied to heat the device to an operational temperature and to the reduction of the carbon dioxide occurring at the cathode side. The device can be used as part of an integrated apparatus in which the carbon dioxide is supplied from a waste stream of a process plant.

RELATED APPLICATIONS

This application is a divisional application of prior U.S. applicationSer. No. 12/961,987, filed Dec. 7, 2010, now allowed, which claimspriority to U.S. Provisional Application Ser. No. 61/325,557, filed onApr. 19, 2010, the entire contents of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producing acarbon monoxide containing product by contacting an electrically drivenoxygen separation device with a carbon dioxide containing feed to reducethe carbon dioxide to carbon monoxide. More particularly, the presentinvention relates to such a method and apparatus in which a hydrocarboncontaining feed is contacted on the anode side of the separation deviceto reduce the partial pressure of oxygen at the anode side and thus,help drive oxygen ion transport and to heat the device to an operationaltemperature at which oxygen ion transport can occur and to supplyendothermic heating requirements to drive the carbon dioxide reduction.

BACKGROUND OF THE INVENTION

There are many known industrial processes that require the use of carbonmonoxide principally in the production of chemicals including themanufacture of aldehydes, methanol, phosgene and acetic acid via theMONSANTO process. Carbon monoxide is also hydrogenated to liquidhydrocarbon fuels in the Fischer-Tropsch process. A common manner ofproducing such carbon monoxide is through steam methane reforming andthe separation of carbon monoxide from resulting synthesis gases inconnection with the production of hydrogen.

Hydrogen has also been produced by natural gas assisted steamelectrolyzers in which steam is contacted at the cathode side of anelectrically driven oxygen separation devices to produce hydrogen fromthe disassociation of water that is assisted by combustion of naturalgas at anode side of the separation device. An example of such a deviceis shown in U.S. Pat. No. 6,051,125. It is to be noted that such devicesare similar to fuel cells save the fact that instead of generatingelectricity, a voltage is applied to drive the oxygen ion transport.

Typically, such electrically driven oxygen separation devices have amembrane element that incorporates an electrolyte layer to conductoxygen ions that is located between two electrode layers to apply anelectrical potential across the electrolyte. The electrode layers areporous and can have sublayers while the electrolyte is an air-tight,dense layer. The resulting composite structure can be in the form of atube in which the oxygen containing feed is fed to the inside of thetube and the separated oxygen is either collected on the outside of thetube and then dissipated. The reverse is possible and oxygen can be fedto the outside of the tube and the permeated oxygen collected on theinside of the tube. Other forms are possible, for example, flat platesand honeycomb-like structures.

The electrolyte layer is formed of an ionic conductor that is capable ofconducting oxygen ions when subjected to an elevated operationaltemperature and an electrical potential applied to the electrode layers.Under such circumstances, the oxygen ions will ionize on one surface ofthe electrolyte layer known as the cathode side and under the impetus ofthe electrical potential will be transported through the electrolytelayer to the opposite cathode side where the oxygen ions will recombineinto molecular oxygen. Typical materials that are used to form theelectrolyte layer are yttria stabilized zirconia and gadolinium dopedceria. The electrical potential is applied to the electrolyte by way ofcathode and anode electrodes. The oxygen ionizes at the cathode and theoxygen ions recombine at the anode. Typically, electrodes can be made ofmixtures of the electrolyte material and a conductive metal, metal alloyor an electrically conductive perovskite. In order to distribute currentto the electrodes, current collectors are utilized in the form of layerson the electrodes opposite to the electrolyte.

As will be discussed, the present invention provides a method ofgenerating carbon monoxide from a carbon dioxide containing feed withthe use of an electrically driven oxygen separation device.

SUMMARY OF THE INVENTION

The present invention provides a method of producing a carbon monoxidecontaining product. In accordance with such method, a cathode side of anelectrically driven oxygen separation device is contacted with a carbondioxide containing feed stream. The carbon dioxide is reduced to thecarbon monoxide through ionization of oxygen at the cathode side andtransport of the oxygen ions to an anode side of the electrically drivenoxygen separation device. The anode side of the electrically drivenoxygen separation device is contacted with a reducing agent streamcontaining a reducing agent to lower partial pressure of oxygen at theanode side of the electrically driven oxygen separation device andthereby to partially drive the oxygen ion transport through theconsumption of the oxygen and reduce voltage and therefore, electricalpower required to be applied to the device and to supply heat to thedevice for purposes of heating the device to an operational temperatureat which oxygen ion transport can occur and to the reduction of thecarbon dioxide occurring at the cathode side. A product streamcomprising the carbon monoxide is withdrawn from the cathode side. Inthis regard, the carbon monoxide product stream could be pure or thecarbon dioxide containing feed stream could also contain water such thatthe product stream is a synthesis gas stream.

The reducing agent stream can be a hydrocarbon containing stream thatcombusts at the anode side. The carbon dioxide containing feed can havea purity of at least about 80 percent by volume of carbon dioxide on adry basis. In such case, the carbon dioxide containing feed stream canbe formed from a waste stream of a process. The process can be, forexample, processes involved in natural gas processing, the production ofmineral products such as cement, lime and soda ash, the production ofmetals such as iron and steel, aluminum, zinc and lead, production ofglass where oxyfuel combustion is used and the production of chemicalssuch as ethanol, ammonia, ethylene oxide and titanium dioxide. The wastestream can be further processed by removing water and other impuritiesfrom the waste stream to produce the carbon dioxide containing feed. Thehydrocarbon containing stream can be methane such that combustionproducts are produced that contain additional carbon dioxide and water.A combustion product stream is extracted from the anode side, water isseparated from the combustion product stream and the combustion productstream is recycled back to the cathode side of the electrically drivenoxygen separation device.

Generally speaking, the reducing agent stream and the carbon dioxidecontaining feed stream are preferably preheated through indirect heatexchange with at least part of the product stream and at least part of areacted stream produced by contacting the anode side with the reducingagent stream and withdrawn from the anode side. Where a hydrocarboncontaining feed stream is used, such feed stream and the carbon dioxidecontaining feed stream are preheated through indirect heat exchange withat least part of the product stream and at least part of the combustionproduct stream. In any method or apparatus of the present invention,part of the product stream can be recycled back to the cathode side forsuch material compatibility purposes as described below and part of thereacted stream or the combustion product stream can also be recycledback to the anode side in order to introduce steam to the anode andprevent carbon deposition.

The method can further include generating a synthesis gas in a blastfurnace and using the synthesis gas as the reactant within the reactantstream.

In another aspect, the present invention provides an integratedapparatus for producing a carbon monoxide containing product thatcomprises a process plant, a heat exchanger, a power supply and anelectrically driven oxygen separation device.

The process plant generates a waste stream containing carbon dioxide,water and other impurities. The heat exchanger is in flow communicationwith the process plant and is configured to preheat a carbon dioxidecontaining stream formed from the waste stream and a reducing agentstream containing a reducing agent through indirect heat exchange with areacted stream and a carbon monoxide containing product stream. Thepower supply is configured to generate an electrical potential and theelectrically driven oxygen separation device has a cathode side and ananode side connected to the power supply such that the electricalpotential is applied to the cathode side and the anode side.

The cathode side is connected to the heat exchanger such that thecathode side is contacted with a carbon dioxide containing feed stream,thereby to reduce the carbon dioxide to the carbon monoxide throughionization of oxygen at the cathode side and transport of the oxygenions to an anode side of the electrically driven oxygen separationdevice and to return the carbon monoxide product stream to the heatexchanger. The anode side is connected to the heat exchanger such thatthe anode side is contacted with the reducing agent stream and thereacted stream is returned to the heat exchanger such that the partialpressure of oxygen is lowered at the anode side and the oxygen iontransport is driven in part through the consumption of the oxygen, theelectrical potential and therefore, electrical power required to beapplied to the electrochemical oxygen separation device is reduced andheat is supplied to the electrochemical oxygen separation device forpurposes of heating the electrochemical oxygen separation device to anoperational temperature at which oxygen ion transport can occur and tothe reduction of the carbon dioxide occurring at the cathode side.

The carbon dioxide containing feed stream can also contain water suchthat the product stream is a synthesis gas stream. Alternatively, thecarbon dioxide containing feed stream can be produced from the wastestream by provision of a drying system positioned between the carbondioxide producing plant and the heat exchanger. The drying system isconfigured to condense the water in the waste stream and separate thewater after having been condensed, thereby to produce a carbon dioxidecontaining feed stream containing about 80.0 percent carbon dioxide on adry basis.

The reducing agent can be methane so that the reacted stream containsadditional water and additional carbon dioxide. The additional water andadditional carbon dioxide are separated in the drying system or anadditional drying system and the additional carbon dioxide is recycledback to the cathode side of the electrically driven oxygen separationdevice. The process plant can be selected from the group of plantsdesigned to expel carbon dioxide comprising natural gas processing, theproduction of mineral products such as cement, lime and soda ash, theproduction of metals such as iron and steel, aluminum, zinc and lead,production of glass where oxyfuel combustion is used and the productionof chemicals such as ethanol, ammonia, ethylene oxide and titaniumdioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims distinctly pointing outthe subject matter that Applicants regard as their invention, it isbelieved that the invention will be better understood when taken inconnection with the accompanying drawings in which:

FIG. 1 is a schematic illustration of an apparatus for carrying out amethod in accordance with the present invention;

FIG. 2 is a schematic illustration of the apparatus of shown in FIG. 1where methane is used as a hydrocarbon containing stream fed to theanode side of an electrically driven oxygen separation device; and

FIG. 3 is a schematic illustration of FIG. 2 integrated with carbondioxide and water generation process.

DETAILED DESCRIPTION

With reference to FIG. 1, an apparatus 1 is illustrated for carrying outa method to generate a carbon monoxide containing product stream 12 froma carbon dioxide containing feed stream 10. The carbon dioxide containedin the carbon dioxide containing feed stream 10 can be of high purity,above 99 percent carbon dioxide by volume or diluted with othersubstances. It is to be noted that where such substances contain oxygen,the carbon monoxide will not only contain such substances, but also,other substances that were molecularly combined with the oxygen. Forexample, if water is present, then hydrogen would be present within thecarbon monoxide containing product stream 12 as a result ofdisassociation of the water molecules at the cathode side 18 of theelectrically driven oxygen separation device 16 described below. Here,the water would be controlled to produce a specific hydrogen to carbonmonoxide ratio in the product which would be a synthesis gas.

The carbon dioxide containing feed stream 12 is introduced into a heatexchanger 14 to preheat the carbon dioxide containing feed stream beforeintroduction into an electrically driven oxygen separation device 16having a cathode side 18 and an anode side 20 separated by a membraneelement 22. An electrical potential is applied to the cathode side 18and the anode side 20 by an electrical power source 24. Electricallydriven oxygen separation device 18 has a structure containing one ormore membrane elements 22 such as described above and although noparticular form of the device is preferred, it can have the form of asolid oxide fuel cell, many examples of which exist in the prior art. Assuch it is to be noted that the term “cathode side” as used herein andin the claims means the side of one or all of such membrane elements inwhich the carbon dioxide is introduced and reduced into carbon monoxideand the term “anode side” means the side of one or all of such elementsin which the reducing agent, for example methane is introduced forpurposes to be discussed. The membrane element 22 or collection ofelements is formed with an electrolyte layer sandwiched between acathode electrode at the cathode side 18 and an anode electrode at theanode side 20. Both of such electrodes are covered with a currentcollector that is physically connected to the electrical power source24.

It is to be noted, that optionally, a part 25 of the carbon monoxidecontaining product stream 12 can be recycled back to the cathode side18. This would be done where the cathode electrode material is notcompatible with the carbon dioxide that may act as an oxidizing agent.For example, if the cathode electrode were made of a Ni/YSZ cermet, thenickel would tend to oxidize in the carbon dioxide containingatmosphere. The recycle of the carbon monoxide will dilute the carbondioxide to prevent the oxidation. The foregoing recycling can beconducted in any embodiment of the invention including those embodimentsshown in FIGS. 2 and 3 below.

The anode side 20 is also connected to the heat exchanger 14 so that areducing agent stream 26 is introduced to the anode side 20 and isreacted so as to produce a reacted stream 28 that is in a heated state.In this regard, the carbon monoxide product stream 12 will also be in aheated state and such streams serve to preheat the carbon dioxidecontaining feed stream 10 and the reducing agent stream 26. The reducingagent stream 26 can be a hydrocarbon containing steam, for example,natural gas or perhaps a low quality syngas produced by a blast furnacethat would contain both hydrogen and carbon monoxide. The presentinvention in such case would be used in effect, to process such streamand convert the low quality and purity carbon monoxide into a highpurity carbon monoxide product. This particular aspect of the presentinvention is intended to be covered in any claim setting forth the scopeof the present invention. The reducing agent stream 26 can also bemethane. In order to prevent carbon deposition in case of the use of ahydrocarbon as a reducing agent, a part 29 of the reacted stream 28which would be a combustion product stream, optionally could be recycledto the reducing agent stream 26 to recycle the steam contained thereinas a result of the reaction. Consequently, if recycling of the carbonmonoxide containing product stream 12 and/or the reacted stream 28 isrequired, then only part of the carbon monoxide containing productstream 12 and/or part of the reacted stream 28 would be available forpreheating purposes. Additionally, such recycling could be performed inconnection with any embodiment of the present invention including theembodiments illustrated in FIGS. 2 and 3 below.

The reducing agent stream 26 reacts at the anode side 20 by consumptionof oxygen to produce heat that heats the membrane element(s) to anoperational temperature, for instance 800° C. to 850° C. and further tosupply heat to the endothermic reaction of the reduction of carbondioxide to carbon monoxide. Since oxygen is being consumed at the anodeside 20, the oxygen partial pressure is lowered to help drive the oxygenion transport through the membrane element(s) 22 and decrease the amountof electrical potential and therefore power that is required to beapplied by electrical power source 24.

More specifically, the reduction of carbon dioxide to carbon monoxideand oxygen is described by the following equation:

$ {{CO}_{2} + {282.3\mspace{14mu}{kJ}\text{/}{mol}}}arrow{{CO} + {\frac{1}{2}O_{2}}} ).$This reaction is endothermic and so at a typical operating temperaturefor the electrically driven oxygen separation unit 16 of 800-850° C.then the reaction enthalpy, ΔH=282.3 kJ needs to be provided per molecarbon dioxide for the reaction to proceed.

Assuming that reducing agent stream 26 were not used, at steady stateoperation the oxygen partial pressure on the cathode side 18 of theelectrolyte is much lower than the anode side and it therefore generatesa voltage. V_(Nernst), given by the following equation

${V_{Nernst} = {{\frac{RT}{4F}\ln\frac{p\; O_{2}^{''}}{p\; O_{2}^{\prime}}} \approx {1\mspace{14mu} V}}};$where R is the gas constant, T is the temperature, F is Faraday'sconstant. This means that at least 1 V needs to be applied to the cellfor the reaction to proceed in the direction of reduction of carbondioxide to carbon monoxide and oxygen. One important operating conditionis the “thermoneutral voltage”, which is the voltage at which all theheat energy required to drive the reduction reaction is provided by theresistive Joule heating of electrically driven oxygen separation device16 and is 1.46 V for the reduction of CO₂ to CO at 850° C. Assumingfurther that thermal energy were recouped in a heat exchanger, such asheat exchanger 14, from the product stream, such as product stream 12and in an oxygen containing stream (since reducing agent stream 26 isnot used) in the carbon dioxide containing feed stream. such as designedherein by reference number 10, the thermoneutral voltage will be ˜1.55V, given that the heat exchange is not 100 percent efficient. In theillustrated embodiments of the present invention, however, no attempt ismade to collect pure oxygen from the anode side 20 of the electricallydriven oxygen separation device 16 and, instead, a reducing agent streamsuch as methane or natural gas is supplied to the anode side 20 where itcombusts with the oxygen transported through the electrolyte of themembrane element(s) 22. This means that the oxygen partial pressure oneither side of the electrolyte is similar so the cell Nernst voltage issmall and the electrochemical reduction of carbon dioxide can be drivenby a much reduced voltage. Combustion of the methane or natural gas inthe anode compartment provides the majority of the thermal energyrequired to drive the endothermic carbon dioxide reduction reaction andthe remainder is supplied through Joule heating by operating theelectrically driven oxygen separation device 16 at 0.51V. The tablebelow demonstrates that this process is a significant net consumer ofCO₂ with only 0.633 ton emitted from electricity generation and methanecombustion for every ton consumed in the reduction process. The overallnet reaction for the process is given by the following equation:3CO₂+CH₄+electrical energy(99 kJ/mol CO₂)→4CO+2H₂O

TABLE Energy & CO₂ balances for Process Configuration of FIG. 2Component Value Energy CO₂ reduction −1781.8 kWh balance Increase gastemperature from −17.7 kWh 800 to 850° C. Thermal losses −88.4 kWhElectrical energy input 624 kWh Thermal energy from natural gascombustion 1263.9 kWh CO₂ CO₂ consumed 2204.6 lb emissions CO₂ emittedfrom electricity generation 836.8 lb CO₂ emitted from combustion ofnatural gas 558.9 lb Net CO₂ emitted −808.9 lb

With reference to FIG. 2, the carbon dioxide containing feed stream 10is of high purity and methane is used as the reducing agent. The methaneis supplied to the anode side 22 where it combusts with the oxygentransported through the electrolyte. As a consequence the product stream12 is of high purity.

With reference to FIG. 3, an integration of Apparatus 1 and a processplant 2 is shown. Process plant 2 generates a waste stream 30 thatcontains water and carbon dioxide, wherein the carbon dioxide is presentin at least about 80 percent by volume on a dry basis, the remainder,for example, argon, oxygen, nitrogen. Process plant 2 can be, forexample, plants used in connection with natural gas processing, theproduction of mineral products such as cement, lime and soda ash, theproduction of metals such as iron and steel, aluminum, zinc and lead,production of glass where oxyfuel combustion is used and the productionof chemicals such as ethanol, ammonia, ethylene oxide and titaniumdioxide. Furthermore, process plant 2 could be a power plant in whichoxy-fuel combustion is conducted to produce a flue gas containing carbondioxide and water.

Water is separated from the waste stream 30 by a drying system 32. Inpractice, drying system 32 would preferably be formed by a water cooledchiller to condense the water within waste stream 30 and aphase-separation pot to separate condensed water in waste stream 30 andthereby form a dried waste stream 34. Where methane is used as thereactant within the reactant stream 26, the reacted stream 28 willcontain water and carbon dioxide. Optionally, the water can be separatedfrom the reacted stream 28 within another drying system 36 to produce arecycle carbon dioxide stream 38 that can be combined with the driedwaste stream 34 to produce the carbon dioxide containing feed stream 10.It is understood that drying system 32 and drying system 36 could becombined into a single system. The recycle of the carbon dioxide is alsopractical in the embodiment shown in FIG. 2. Furthermore, drying system32 could be deleted or controlled so that the water is introduced intothe electrically driven oxygen separation device 16 to produce hydrogenalong with the carbon monoxide and therefore a synthesis gas product.The drying system 36, if present could be similarly controlled.

We claim:
 1. An integrated apparatus for producing a carbon monoxidecontaining product comprising: a process plant comprising a waste streamcontaining carbon dioxide; a power supply configured to generate anelectrical potential; an electrically driven oxygen separation devicehaving a cathode side and an anode side connected to the power supplysuch that the electrical potential is applied to the cathode side andthe anode side; a carbon dioxide containing feed stream produced fromthe waste stream and supplied to the cathode side; a carbon monoxidecontaining product stream generated by the reduction of the carbondioxide feed stream to carbon monoxide through ionization of oxygen atthe cathode side and transport of oxygen ions to the anode side of theelectrically driven oxygen separation device; a reducing agent streamcontaining a reducing agent supplied to the anode side; a reacted streamformed from the reducing agent stream at the anode side; a heatexchanger in flow communication with the process plant, wherein the heatexchanger is connected to the cathode side to preheat the carbon dioxidestream produced from the waste stream and to return the carbon monoxidecontaining product stream from the cathode side to the heat exchangerand connected to the anode side to preheat the reducing agent streamcontaining the reducing agent and to return the reacted stream to theheat exchanger from the anode side wherein the preheat is achievedthrough indirect heat exchange with the reacted stream and the carbonmonoxide containing product stream; wherein the partial pressure of theoxygen is lowered at the anode side and the transport of oxygen ions isdriven in part through the consumption of the oxygen, thereby loweringthe electrical potential and therefore, reducing electrical powerrequired to be applied to the electrochemical oxygen separation device;and wherein heat is supplied to the electrochemical oxygen separationdevice for purposes of heating the electrochemical oxygen separationdevice to an operational temperature at which oxygen ion transport canoccur.
 2. The integrated apparatus of claim 1, wherein the carbondioxide containing feed stream also contains water such that the productstream is a synthesis gas stream.
 3. The integrated apparatus of claim1, wherein the carbon dioxide containing feed stream is produced fromthe waste stream by provision of a drying system that is positionedbetween the process plant and the heat exchanger, the drying systemconfigured to condense the water in the waste stream and separate thewater after having been condensed, thereby to produce a streamcontaining about 80.0 percent carbon dioxide on a dry basis as thecarbon dioxide containing feed stream.
 4. The integrated apparatus ofclaim 3, wherein: the reducing agent is methane so that the reactedstream contains additional water and additional carbon dioxide; theadditional water and additional carbon dioxide are separated in thedrying system or an additional drying system; and the additional carbondioxide is recycled back to the cathode side of the electrically drivenoxygen separation device.
 5. The integrated apparatus of claim 1 orclaim 2 or claim 3 or claim 4, wherein the process plant is selectedfrom the group of plants designed to expel carbon dioxide comprisingnatural gas processing, the production of mineral products such ascement, lime and soda ash, the production of metals such as iron andsteel, aluminum, zinc and lead, production of glass where oxyfuelcombustion is used and the production of chemicals such as ethanol,ammonia, ethylene oxide and titanium dioxide.